Aviation fuel is vulnerable to contamination from a number of sources through the fuel distribution system. Contamination takes many forms, from trail-back in pipeline systems, to leaking roofs in holding tanks, or to treatment by wrong (non-approved) additives. Since the ultimate goal of the aviation fuel system is to deliver 100% “fit for purpose” fuel to the skin of the aircraft, it is essential that contamination problems, which arise along the fuel distribution path, be rapidly assessed.
One contamination issue that must be reduced to a minimum level is free water in fuel. Free water can result in microbiological growth in aircraft fuel tanks, poor engine performance or, at worst, a complete failure of the aircraft's ability to safely operate. Free water in an aircraft fuel system is removed by water separator coalescence filters or by still-tanking fuel until gravity causes the water (specific gravity about 1.0) to separate out of the aviation fuel (specific gravity about 0.8) and collect at the bottom of the tank or other container. Modern airport fueling systems often include coalescers which remove free water, prior to fuel reaching the skin of the aircraft. Modern filter coalescers use a variety of materials to accomplish the separation of free water. At the time of this writing, water filter-coalescers approved for use by the American Petroleum Institute (API) employ materials specified by the API 1581 standard (5th Edition). These materials are typically special fiber-type polymer materials. The performance of these filter materials can be adversely affected by chemicals in aviation turbine fuel (jet fuel), often referred to as “surfactants.” Surfactants are surface-active chemicals which impair the ability of coalescer materials to aggressively remove free water. This chemical deterioration of filter performance is referred to, in the industry, as “disarming” the water filter. Hence, the ability to test fuels as to their chemical interaction behavior in modern API 1581 filter-coalescers is an essential element of safe operation of aircraft fueling operations worldwide. The goal of filtering is to supply fuel to the aircraft that meets all aircraft specifications. Aviation turbine fuel cleanliness specifications are set forth in two main standards. One widely recognized standard is overseen by the ASTM International (formerly American Society for Testing & Materials) specification D1655-14. A second standard is managed by the British Ministry of Defense: specification DefStan 91-91. There are also related standards for specialized fuels, for example: the United States Department of Defense MIL-DTL-83133 for JP-8 type fuel. I have invented a system and method, by which a small sample of a specific fuel is evaluated in a rapid and fully automatic laboratory instrument, to accurately access if that sample contains harming surfactants that may affect the water separation performance of large field-deployed filter coalescers. This system and method can be adapted for use with newer filter materials as the API 1581 5th edition specifications change to subsequent editions of the standard (see www.API.org). Note, although as described herein for surfactant testing in aviation turbine fuel, the instrument can also determine surfactant level effects on water separation characteristics of other distillate fuels, for example, of diesel fuel.
Water separation instruments (“Separometers”) are commonly categorized as either “large scale”/“full-scale” (bulky and stationary) or “small-scale” (portable). Making a “small-scale” instrument as accurate as a “full-scale” instrument has been regarded as technically difficult. The method of the present invention relates to the preconditioning of the filter in a small-scale separometer. Modern fuel-filter “stands” operate for long periods of time, often without the presence of any free water. “Stand” is an industry term which refers to a set of filters that are used to treat fuel at a specific location, as the fuel moves through a delivery system. For example, in the United States, a Jet Fuel Filter Stand typically consists of three sequentially arranged filter vessels: first a clay treating vessel, then a coalescer vessel, and finally a particulate vessel. In fact, this is the normal operating condition, since modern fuel delivery systems are often equipped with free water removal filters or methods throughout the distribution system. In fact, the fuel delivery system is often described by industry insiders as “over-filtered.” Surfactants are detergents, surface active chemicals, which will chemically behave differently in the presence of water. Surfactant occurrence in fuels can be the result of byproducts of the crude oil refining process, or they could be subtle side-effects of approved additives, or worse, from the addition of non-approved additives. Fuel additives are commonly used to modify the performance or physical characteristics of fuels. For example, Static Dissipative Additive (SDA), which is added to improve the electrical conductivity of fuel and to reduce the potential for electrostatic build-up of electrical charge in fuel, is also known in the industry to behave as a weak surfactant. When in the presence of free water, these surfactant chemicals are much more likely to react with the highly-polarized water molecules than with the fuel itself. Hence, water actually tends to reduce interaction between surfactants and the surface of the filter media. Hence, the “reactivity” (the ability to disarm a filter coalescer) of these surfactant chemicals changes, as the availability of free water in the subject fuel changes.
Traditional water separation determination instruments, which measure the ability of water to be coalesced, have not taken into account this water reactivity of surface-active ingredients. In fact, the current prevalent test (ASTM D3948), for determining potential surfactant levels in fuel, first mixes the fuel/surfactant with a high level of free “challenge” water, ˜1000 ppm, to form an emulsion. This emulsion of water/fuel/surfactant is then presented to the test filter medium. However, in this test, since the test fuel/surfactant has already been mixed with the challenge water, in high concentration, the available surfactants may not react with the filter material to the same extent as they would without the presence of the filter challenge water. This mixing of water into the test fuel impairs the ability of the existing determination method, as described by ASTM D3948, to accurately predict whether or not a particular test fuel will disarm field water filter-coalescers.